Infrared temperature sensor and control for use with heated, moving bodies

ABSTRACT

A temperature sensor is provided for measuring infrared radiation from a heated, moving processing device. The measurement is made from a &#39;&#39;&#39;&#39;black body&#39;&#39;&#39;&#39; cavity extending within the device being measured and so provides greater accuracy of readings. If the device being measured is cylindrical and rotates, the cavity is along the edge of the rotational surface and may be subdivided so as to provide a chopper for the readings. Control circuitry associated with the infrared detector allows the sensor to control heating elements within the device.

United States Patent Poole et al.

[451 Apr. 4, 1972 [54] INFRARED TEMPERATURE SENSOR AND CONTROL FOR USEWITH HEATED, MOVING BODIES [72] Inventors: Richard R. Poole; David D.Bulkley, both of Norwalk, Conn.

[73] Assignee: lrtronlcs, Inc., Stamford, Conn.

[22] Filed: July 15, 1969 [21] Appl. No.: 841,861

[52] US. Cl. ..73/35l, 73/355 R [51] Int. Cl. ....G0lj 5/62, GOlk 13/08[58] FleldotSearch ..73/l F, 351,355

[56] References Cited UNITED STATES PATENTS 3,527,097 9/1970 Deczky..73/35l 3/1939 Mead ..73/355X Engborg ..73/355 X Primary Examiner-LouisR. Prince Assistant Examiner-Frederick Shoon Attorney-Bryan, Parmelee,Johnson & Bollinger ABSTRACT A temperature sensor is provided formeasuring infrared radiation from a heated, moving processing device.The measurement is made from a black body" cavity extending within thedevice being measured and so provides greater accuracy of readings. Ifthe device being measured is cylindrical and rotates, the cavity isalong the edge of the rotational surface and may be subdivided so as toprovide a chopper for the readings. Control circuitry associated withthe infrared detector allows the sensor to control heating elementswithin the device.

13 Claims, 7 Drawing Figures PATENTEDAPR 41912 3,653,263

SHEET 1 [1F 3 INVENTORS RICHARD R. POOLE O D W) ATTORNEYS PATENTEDAPR41972 3,653,263

sum 2 UF 3 FIG. 5 I lNVENTORS RICHARD R. POOLE DAVID D. BULKLEY ATTOR NEYS PAIEIIIEIIIIII 4R2 8,653,263

SHEET 3 UF 3 48(OR 2o) INFRA 22 RED DETECTOR HEATER 55 9 AMPLIFIER 5e\57 II A METER PowER CONTROL PowER SUPPLY 59 FOR HEATERS RICHARD R. POOLEINvENToRs FIG. 7

' DAvID D. BULKLEY BY mg ATTORNEYS INFRARED TEMPERATURE SENSOR ANDCONTROL F OR USE WITH HEATED, MOVING BODIES SUMMARY OF THE INVENTIONThis invention deals with the measurement and control, through infrareddetection, of the temperature of various devices used for heat treatmentof materials. In particular, it is directed to moving processing devicessuch as heated rolls, in which the temperature must be carefullycontrolled. An example would be a heated roll used for processingsynthetic fibers.

The temperature measurement made for use in control is not a directcontact measurement of the temperature of the object itself, but is anon-contact measurement of the infrared radiation emitted by the body.Since the emitted radiation is a function of the temperature of thebody, the radiation detector may be calibrated to control actualtemperature. By using the infrared radiation and detection method ofthis invention, greater accuracy, reliability, and repeatability ofcontrol are often achieved. The frictional problems associated withcontact temperature measurement of moving bodies are eliminated.

Other devices using infrared radiation as a method of temperaturedetermination and control of moving bodies have, of course, been used inthe past. To the best of our knowledge, however, in each instance thesedevices measured an exposed surface of the object and so were subject topossible errors as the surface conditions changed through corrosion,dirt, etc. An example of one such device is given in Troll US. Pat. No.3,369,106.

In the present device, by contrast, the external surface is not used asa source of infrared radiation. Rather, a cavity or slot is milled orbored in an area of the heated device itself proximate to the area whereit is desired to measure the temperature. The cavity is located where itwill not affect the function of the device and is so positioned as tocontinually or periodically be sensed by a detector as the body moves.If the cavity is of sufficient depth relative to its width, the infraredradiation received from inside this opening will approach that of aperfect or black body" radiator. This depth is normally at least 4 timesthe minimum width.

This invention can be used in many types of rotating structures. It isillustrated here in terms of a heated rotating roll. The roll has acavity in the shape of a slot along its periphery and running parallelto the axis of the roll. An infrared detector is pointed into the slotand so takes a reading of the infrared radiation coming from the slot.

The edge of the roll having the slot may have a cover plate interruptingthe slot periodically so as to act as a chopper. Heating elements of anydesired type may be placed within the roll and be controlled bycircuitry actuated by the infrared detector.

THE DRAWINGS The drawings illustrating this invention include:

FIG. 1 is a side elevation, partly broken away, of a first form of theinvention. In this form the cavity is a slot in the periphery of thecylinder or roll; and the chopper, if one is used, is integral with theinfrared detector.

FIG. 2 is a perspective view of the edge of the roll partially brokenaway to show the slot.

FIG. 3 is a partial side elevation of another form of the invention, theelevation being partially broken away to show more details of thestructure. In this form, the slot in the roll is periodicallyinterrupted to produce a chopper effect. The driving mechanism is notshown in FIG. 3, but is like that of FIG. 1.

FIG. 4 is an exploded perspective showing the construction of the rolland the cylindrical slot.

FIG. 5 shows a detail of one portion of the cylinder broken away to showthe cross-sectional structure.

FIG. 6 is a further modification showing a radiation interruptor on thesurface of a rotating heated body.

FIG. 7 is a simplified control circuit diagram showing how the detectorwould be used to control the heating elements for the object beingheated.

DETAILED DESCRIPTION OF THE INVENTION Structure The invention, as shownherein, is used to control the temperature of a heated roll or drum. InFIG. 1 the roll is identified by the numeral 1. It is mounted on a shafi2 about which it may rotate, the shaft passing through a supportingframe 3 to a coupling 4 and thence to a motor 5. If desired, reducinggears may be placed between motor 5 and shalt 2.

Located within the roll 1 and secured to frame 3 are heating elements 8and 9. These elements may be of any desired type, but preferably arequartz heating elements. These elements are connected to a power supply(not illustrated) through leads 10 and 11 respectively.

The edge of roll 1 which faces frame 3 has milled in it a slot or groove17. Slot 17 is proximate to, but beneath, the surface the temperature ofwhich is to be controlled and has an open end. This slot provides theblack body" cavity, referred to above, that is the source of theinfrared radiation. Normally a slot or opening will act as asubstantially perfect black body radiator, or approach being one, if ithas a ratio of length to minimum width of at least 4 to 1. In thepractice of this invention such a ratio is preferable. Length, in thisinstance, is the dimension of the slot which is parallel to the axis ofthe roll, i.e., the direction seen by the detector. The minimum widthwould be that measured across the slot.

Since groove 17 is formed along the entire periphery of roll 1, it willhave a cylindrical configuration and the same axis as drum 1. The endopening of the groove will face outwardly in a direction parallel to theaxis of the roll.

The infrared energy radiated from slot 17 will be, as is well known, afunction of the temperature of roll 1 and, in particular, a function ofthe temperature of the portion of the roll defining the bottom of slot17. Thus, such a slot along the edge of the roll will emit infraredradiation which when detected and amplified, will produce an electronicsignal which is a function of roll surface temperature. A more accuratereading will be obtained if the slot penetrates to a depth in the rollsuch that its end is right under the working surface. Though this ispreferred, it may, in some instances, present structural problems and bea limitation on how deep the slot can go into the roll. The slot should,however, be near enough the desired surface portion so that the infraredradiation detected is functionally related to the surface temperature,i.e., the slot will, in some way, always be a function of surfacetemperature no matter how deep it is.

Though the slot is shown in cross-section in FIG. 1 it will be realizedfrom FIG. 2 that the slot extends all the way around the periphery ofthe roll.

An infrared detector 20 is mounted adjacent to the periphery of the rollto sense the radiation from the slot. As shown in FIG. 1, detector 20 ismounted on supporting frame 3 over an opening 21 in the frame and facingthe slot. It is on the opposite side of the frame from cylinder 1.Opening 21 is positioned directly over a portion of slot 17 in drum 1permitting infrared detector 20 to view the inside of slot 17 throughopening 21 in frame 3.

Infrared detector 20 may be of any conventional type, such as a leadsulphide detector. It has a chopper" as part of the unit. (A chopper isa well known device for periodically blocking the radiation passing froman infrared radiator to an infrared detector, and so provides greateraccuracy in the readings and improved background discrimination.Choppers as such are described in various publications, such as InfraredRadiation by Henry L. Hackforth, 1960, beginning at page 95). The outputfrom the infrared detector 20 passes through leads 22 to the amplifier55 where it is amplified and converted into an on-off or proportionalsignal. This signal then passes by lead 56 to power control 58 forcontrol of power to heaters 8 and 9 (See FIG. 7).

A modification of this structure is shown in FIGS. 3, 4 and 5. Thismodification, in essence, involves the discovery that, when a movingsurface or cavity, especially a rotating one, is used as the infraredsource for an infrared radiation reading, the surface or cavity on themoving device itself may be interrupted to accomplish the function of achopper. The interruption should be accomplished by something integralwith the moving device, such as the use of highly non-radiating, i.e.,reflective, paint or plating, the use of a covering chopper mask thatwill regularly and periodically block or greatly reduce the radiationbeing detected, or interrupted milling of groove 17. This permits usingan infrared detector without a separate chopper andpermits reduction insize. A preferred form of interrupter is chopper plate 32 of FIGS. 3, 4and 5.

(Since most of the elements of FIGS. 3, 4 and are similar to those ofFIGS. 1 and 2, similar numbers will be used to identify structure whereappropriate. Description, where it would be repetitive, will not berepeated.)

In the modification of FIGS. 3, 4 and 5 a rotating roll 1 is mountedupon a shaft 2. The roll includes a slot 17 along the edge which facesthe frame 3, the slot being of sufficient depth relative to its minimumwidth to be effectively a black body radiator. The-roll 1 has a flangeor lip 30 extending radially outwardly along the peripheral edge outsideslot 17. This lip 30 serves as a base to which an aperture or chopperplate 32 may be secured. Plate 32 fits over the end of roll 1 and issecured by metal screws or bolts through holes 33, in the cover 32, and34 in lip 30. Preferably a disc or gasket 36, made of an insulatingmaterial such as asbestos and having the same shape and hole pattern asplate 32 is sandwiched between plate 32 and roll 1 to minimize heattransfer.

Plate 32 is generally ring-shaped and has a central opening 40corresponding to the central opening on the end of roll 1. 'It also hasa series of slots 42 at the same radial distance from its axis as slot17 is from the axis of roll 1. These slots 42 are arcuate'in shape andare spaced intermittently around the circumference of plate 32. They areso positioned as to expose portions of slot 17 when plate 32 is mountedon roll 1.

Slots 42 are regularly spaced around plate 32 and preferably exposeexactly half of slot 17. Slots 42 are all of the same length; and allthe spaces 43 between the slots, which cover slot 17, are of the samelength. Spaces 43 may, but do not necessarily have to be, equal inlength to the length of slots 42. .Thus, with this regular spacing, slot17 is covered part of the time, and as roll 1 rotates, slot 17 isuncovered for equal and regular time periods, as viewed by stationarydetector 48. The result is that chopper plate 32, because integral withthe radiating device, can act as a chopper producing a pulsed outputwhileroll l is rotating.

As a result of the modification of FIGS. 3, 4 and 5, there is no needfor a combined infrared detector and chopper such as in FIG. 1. Insteadof that a simple infrared detector 48 connected to the amplifier andcontrol is all that is necessary. This allows the unit to be morecompact. It also eliminates the problem of chopper failure sometimesfound in high temperature industrial equipment.

For greatest capability, plate 32 should have the minimum radiationefficiency, thus giving it the greatest contrast with radiation receivedfrom slot 17 through openings 42. Therefore, it is best to have theexposed surface of plate 32 chrome plated at like. Similarly, tominimize the conductive heat transmission from roll 1 to plate 32, it isbest to have an insulating gasket 36 mounted between roll 1 and plate32. Gasket 36 should have openings corresponding to those of plate 32 sothat it does not interfere with thechopping effect.

Any number of slots 42 may be used as long as they are of equal lengthand regularly spaced. The slots must, however, each be sufficiently longsuch that for a maximum desired rate of rotation of roll 1, infrareddetector 48 will have an opportunity to satisfy-its required rise time.That is, if the slots 42 are so short relative to the rate of rotationthat each exposure of detector 48 to groove 17 is for less time than theinternal rise time of detector 48, an inaccuracy in reading may result.

FIG. 6 shows another form of interrupter, usable when the infrareddetector receives radiation from the surface of a heated rotating bodyrather than from a cavity. Here a rotating roll 50 has a detector 51positioned adjacent its surface to receive radiation. On the roll,beneath detector 51 are a series of regularly spaced, equal black bodyareas. These are formed by providing alternating light 52 (highlyreflective) and'dark 53 (highly radiative, i.e., black body) areas orsections. These serve as an interrupter or chopper for radiated infraredenergy as roll 50 rotates and so produce pulses of radiation. The rateof pulsing is dependent upon the rate of rotation of the body and, ofcourse, upon the number of said areas.

Other forms of interrupter can also be used, whether on a rotatingsurface or covering a rotating cavity, just as long as they are integralwith the rotating body and provide for regular interruption so that thedetector has a base line for reading. Preferably, the pulses producedwill each have a duration greater than the rise time of the detector.

A diagram showing the control circuitry is given in FIG. 7 (the figurealso includes the upper portion of FIG. 3). Infrared detector 48,mounted on frame 3 so that it can take readings through hole 21, has itsoutput fed through lead 22- to an amplifier. The amplifier 55 should besufficiently broad band such that it can amplify,- without distortion,the entire range of frequencies created by the chopper plate 32 over theanticipated speeds of rotation of roll 1. The output of amplifier 55passes through lead 56 to heater control 58. The other input to theheater control is from a power supply on lead 59. Heater control 58 isadapted to cut off or reduce the power input to the heaters 8 and 9through-leads I1 and 10 respectively when the temperature of roll 1, asindicated by the amount of infrared radiation detectedtends to get toohot, and to increase the power or turn it on when the temperature tendsto get too low. Thus, an automatic control is provided.

The output of amplifier 55 may also go to meter 57 to give a directtemperature reading.

The circuit would be similar for the structure of FIG. 1, except that acombined detector and chopper 20 would be used instead of detector 48.

Operation The overall method of operating the system is substantiallythe same as that of other infrared detection and control systems.Infrared radiation is detected through a calibrated detector, and theresulting output is used to control the heating units. The difference inoperation between this system and prior systems lies in the place ofdetection, that is a cavity or peripheral slot providing black bodyradiation, and in the use of an interruptor integral with the black bodyradiator to create a chopper.

The unit of FIGS. 1 and 2 operates by supplying power to the heaters 8and 9 through leads 10 and 11 and actuating motor 5 to rotate roll 1.Infrared radiation of an amount related to the temperature of roll 1, isproduced by the drum. For present purposes, however, the importantradiation is that coming from slot 17 on the edge of the roll. Slot 17has its open side facing to the right as shown in FIG. 1 and a portionof slot 17 is always facing opening 21 in frame 3. A portion of theradiation passes from slot 17 through opening 21 and into the infrareddetector .48. In the structure of FIG. I detector 20 preferably includesa chopper. The output from detector 20 passes through lead 22 and toamplification and control circuits, like those of FIG. 7 and the controlcircuit determines the amount of power necessary to be supplied to theheaters so that the desired temperature is reached and maintained withinthe desired narrow limits.

The unit must, of course, first be calibrated so that the detectedradiation is correlated with the temperature of the surface. This can bedone by any of the normal methods.

In addition to control, the output of the detector may also go to meter57 to give a direct temperature reading.

The unit of FIGS. 3, 4 and 5 operates in the same manner as that ofFIGS. 1 and 2 except for the chopping action. In the unit of thosefigures a simple infrared detector 48 is used, facing opening 21, whichdoes not include a separate chopper. Rather the chopping is achieved bythe rotation of roll 1 by motor 5 and the regular and periodic openingand closing of slot 17 by the slots 42 and intervening spaces 43 onchopper plate 32. This provides a chopper that is integral with roll 1,directly related to the speed of rotation of roll 1, and, of course,coordinated with its rotation. The speed of operation of the chopper isa function of the speed of rotation of roll 1, but the total exposure ofdetector 48 to radiation remains constant.

The modification of FIG. 6 operates by having the alternate areas 52 and53 produce pulses of radiation for detector 51. Use of the detectedradiation is the same as for FIGS. 3, 4 and 5.

By way of example of chopper frequency that may be used, chopper plate32 of FIGS. 3, 4 and 5 includes eight slots 42 around the circumferenceand eight corresponding and equal intervening spaces 43, giving eightcycles of chopping for each revolution of roll 1. In a typical operationroll 1 may rotate 4,000 revolutions per minute or approximately 66.7 persecond. This, then, would give a chopping frequency of 8 X 66.7 or about533 cps. It will be noted that the chopping frequency is a function ofrotation speed, but that the total emitted radiation received by thedetector is independent of speed.

By use of this method, a more sensitive temperature component can beobtained. The faster response permits more rapid control of the heatingelements, and so a more closely controlled roll temperature.

The foregoing shows the preferred embodiments of the invention.Naturally the concepts may be used in other forms without departing fromits spirit.

What is claimed:

1. The method measuring temperature of the surface of a rotating body,said body having a cylindrical configuration and rotating about itsaxis, and said body having a groove along one edge thereof defining ablack body radiator, said method including the steps of positioning aninfrared detector adjacent to said groove to detect and measure infraredradiation from said groove while said body is rotating, and thereafterusing said detected and measured radiation as a measure of thetemperature of said surface.

2. Apparatus for determining the surface temperature of a moving body byuse of infrared emissions, said apparatus including said moving bodywith said surface, said body having an open-ended cavity thereinadjacent said surface and moving therewith but not interrupting saidsurface, said moving cavity defining an infrared radiator, an infrareddetector positioned adjacent said moving cavity to receive and measureinfrared radiation from said moving cavity, said detector beingcalibrated relative to the temperature of said surface, whereby saiddetector may determine the surface temperature of said body bymeasurement of said infrared radiation, said body being rotatable andincluding an interrupter integral with said body and positioned oversaid cavity to cause said radiation to be pulsed when said body is inmotion.

3. Apparatus as set forth in claim 2 in which said body is a cylindricalroll, said surface is the outer surface of said drum, and said cavity isa cylindrical groove beginning at one edge of said roll.

4. Apparatus as set forth in claim 3 including a chopper plate mountedon said edge and over said groove, said plate having openings thereinpartially exposing said groove, said openings being of uniform lengthand regularly spaced over said groove, whereby, when said roll isrotated, said plate will act as an infrared chopper to produce a pulsedoutput in said detector.

5. Apparatus as set forth in claim 4 in which said chopper plate has amirrored surface on the side thereof facing said detector to reduceradiation and including a thermally-insulating gasket between said plateand the edge of said roll.

6. Temperature determination apparatus for measurement of thetemperature of the surface of a rotating heated roll, including a groovein one edge of said roll, said groove extending into said roll to apoint sufficiently proximate to said surface so that said groove willemit infrared radiation in an amount functionally related to thetemperature of said surface, an infrared detector adjacent said groovefor measuring infrared radiation being emitted therefrom, said detectorbeing calibrated relative to said surface temperature whereby saiddetector may be used to determine the temperature of said surface.

7. Apparatus as set forth in claim 6 in which said groove is sodimensioned as to be substantially a black body radiator and in whichsaid detector is positioned so as to receive radiation from the bottomof said groove.

8. Apparatus as set forth in claim 6 including an interrupter integralwith said roll to interrupt said groove periodically so that, as saidroll is rotated, the infrared emissions received by said detector arepulsed.

9. Apparatus as set forth in claim 8 in which said interrupter is achopper plate mounted on the edge of said drum and over said groove,said plate having evenly-spaced openings therein exposing portions ofsaid groove.

10. In an infrared detection system for determining the temperature of aheated rotating body having an infrared radiating section, thatimprovement including a detector positioned relative to said body so asto receive infrared radiation from said section, an interrupterassociated with said section and integral with said heated body toregularly interrupt said infrared radiation from said section andthereby pulse the radiation received by said detector, said rate ofpulsing being dependent upon the rate of rotation of said body.

11. In an infrared detection system as set forth in claim 10, thatimprovement in which said radiating section is a cavity in said heatedbody.

12. In an infrared detection system as set forth in claim 11, thatimprovement in which said interrupter is a reflective plate partiallycovering said cavity.

13. In an infrared detection system as set forth in claim 10, thatimprovement in which said radiating section is a portion of the surfaceof said heated body and said interrupter is a means on said surface forregularly varying the intensity of infrared radiation from said portionas said body rotates.

* IF l

1. The method measuring temperature of the surface of a rotating body,said body having a cylindrical configuration and rotating about itsaxis, and said body having a groove along one edge thereof defining ablack body radiator, said method including the steps of positIoning aninfrared detector adjacent to said groove to detect and measure infraredradiation from said groove while said body is rotating, and thereafterusing said detected and measured radiation as a measure of thetemperature of said surface.
 2. Apparatus for determining the surfacetemperature of a moving body by use of infrared emissions, saidapparatus including said moving body with said surface, said body havingan open-ended cavity therein adjacent said surface and moving therewithbut not interrupting said surface, said moving cavity defining aninfrared radiator, an infrared detector positioned adjacent said movingcavity to receive and measure infrared radiation from said movingcavity, said detector being calibrated relative to the temperature ofsaid surface, whereby said detector may determine the surfacetemperature of said body by measurement of said infrared radiation, saidbody being rotatable and including an interrupter integral with saidbody and positioned over said cavity to cause said radiation to bepulsed when said body is in motion.
 3. Apparatus as set forth in claim 2in which said body is a cylindrical roll, said surface is the outersurface of said drum, and said cavity is a cylindrical groove beginningat one edge of said roll.
 4. Apparatus as set forth in claim 3 includinga chopper plate mounted on said edge and over said groove, said platehaving openings therein partially exposing said groove, said openingsbeing of uniform length and regularly spaced over said groove, whereby,when said roll is rotated, said plate will act as an infrared chopper toproduce a pulsed output in said detector.
 5. Apparatus as set forth inclaim 4 in which said chopper plate has a mirrored surface on the sidethereof facing said detector to reduce radiation and including athermally-insulating gasket between said plate and the edge of saidroll.
 6. Temperature determination apparatus for measurement of thetemperature of the surface of a rotating heated roll, including a groovein one edge of said roll, said groove extending into said roll to apoint sufficiently proximate to said surface so that said groove willemit infrared radiation in an amount functionally related to thetemperature of said surface, an infrared detector adjacent said groovefor measuring infrared radiation being emitted therefrom, said detectorbeing calibrated relative to said surface temperature whereby saiddetector may be used to determine the temperature of said surface. 7.Apparatus as set forth in claim 6 in which said groove is so dimensionedas to be substantially a black body radiator and in which said detectoris positioned so as to receive radiation from the bottom of said groove.8. Apparatus as set forth in claim 6 including an interrupter integralwith said roll to interrupt said groove periodically so that, as saidroll is rotated, the infrared emissions received by said detector arepulsed.
 9. Apparatus as set forth in claim 8 in which said interrupteris a chopper plate mounted on the edge of said drum and over saidgroove, said plate having evenly-spaced openings therein exposingportions of said groove.
 10. In an infrared detection system fordetermining the temperature of a heated rotating body having an infraredradiating section, that improvement including a detector positionedrelative to said body so as to receive infrared radiation from saidsection, an interrupter associated with said section and integral withsaid heated body to regularly interrupt said infrared radiation fromsaid section and thereby pulse the radiation received by said detector,said rate of pulsing being dependent upon the rate of rotation of saidbody.
 11. In an infrared detection system as set forth in claim 10, thatimprovement in which said radiating section is a cavity in said heatedbody.
 12. In an infrared detection system as set forth in claim 11, thatimprovement in which said interrupter is a reflective plate partiallycovering said cavity.
 13. In an infrared detection system as set forthin claim 10, that improvement in which said radiating section is aportion of the surface of said heated body and said interrupter is ameans on said surface for regularly varying the intensity of infraredradiation from said portion as said body rotates.